Perlut Noah, Maxwell Logan M, Kovach Adrienne, Parker Patricia, Renfrew Rosalind B
School of Marine and Environmental Programs University of New England Biddeford Maine USA.
Department of Natural Resources and the Environment University of New Hampshire Durham New Hampshire USA.
Ecol Evol. 2023 Jan 16;13(1):e9697. doi: 10.1002/ece3.9697. eCollection 2023 Jan.
Little is known about the causes and consequences of alternative pathways flown by long-distance migratory birds. Bobolinks () breed in grasslands across northern North America and migrate from their breeding grounds toward the eastern Atlantic Coast and then proceed through the Caribbean to South America. However, a small but regular number of Bobolinks have been recorded on the Galapagos Islands. We collected genetic samples from nine Galapagos Bobolinks and performed double-digest restriction site-associated sequencing. We compared them with samples from seven locations across their breeding distribution to determine their population of origin. Galapagos Bobolinks shared the genetic structure of a cluster in the eastern portion of the breeding range that includes New Brunswick and Ontario, Canada, and Vermont, United States. Genetic assignment tests largely corroborated this finding, although slightly different results were obtained for the two methods. All individuals were assigned to the Ontario breeding population using AssignPop, while Rubias assigned six of the migrants to Ontario and three to a Midwest breeding population. Low average relatedness among Galapagos individuals indicates that they are not more related to one another than to individuals within a breeding population and are therefore likely not from a single, small isolated population. Our results do not support the probability hypothesis-that Galapagos Bobolinks originated from the region that includes the greatest proportion of their breeding range (Great Plains)-or the vagrant hypothesis-that migrants are displaced onto Galapagos due to weather events. Instead, our findings support the proximity hypothesis, where migrants originate from the geographically closest-breeding populations.
对于长途候鸟所采用的替代路线的成因和后果，我们知之甚少。食米雀（）在北美北部的草原繁殖，从繁殖地向大西洋海岸东部迁徙，然后穿过加勒比地区前往南美洲。然而，在加拉帕戈斯群岛记录到少量但数量稳定的食米雀。我们从9只加拉帕戈斯食米雀身上采集了基因样本，并进行了双酶切限制性位点关联测序。我们将它们与来自其繁殖分布范围内7个地点的样本进行比较，以确定它们的起源种群。加拉帕戈斯食米雀与繁殖范围东部一个集群的遗传结构相同，该集群包括加拿大的新不伦瑞克省和安大略省以及美国的佛蒙特州。基因分配测试在很大程度上证实了这一发现，尽管两种方法得到的结果略有不同。使用AssignPop将所有个体都分配到安大略繁殖种群，而Rubias将6只迁徙个体分配到安大略，3只分配到中西部繁殖种群。加拉帕戈斯个体之间的平均亲缘关系较低，这表明它们彼此之间的亲缘关系并不比繁殖种群内的个体更密切，因此可能并非来自一个单一的、小型孤立种群。我们的结果不支持概率假说——即加拉帕戈斯食米雀起源于其繁殖范围占比最大的地区（大平原）——也不支持流浪假说——即迁徙个体因天气事件而流离到加拉帕戈斯群岛。相反，我们的研究结果支持邻近假说，即迁徙个体起源于地理上最接近的繁殖种群。
